rnbd-clt: open code send_msg_open in rnbd_clt_map_device

Let's open code it in rnbd_clt_map_device, then we can use information
from rsp to setup gendisk and request_queue in next commits. After that,
we can remove some members (wc, fua and max_hw_sectors etc) from struct
rnbd_clt_dev.
Acked-by: Jack Wang <jinpu.wang@ionos.com>
Signed-off-by: Guoqing Jiang <guoqing.jiang@linux.dev>
Link: https://lore.kernel.org/r/20220706133152.12058-2-guoqing.jiang@linux.devSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/rnbd/rnbd-clt.c

@@ -1562,7 +1562,14 @@ struct rnbd_clt_dev *rnbd_clt_map_device(const char *sessname,
 {
 	struct rnbd_clt_session *sess;
 	struct rnbd_clt_dev *dev;
-	int ret;
+	int ret, errno;
+	struct rnbd_msg_open_rsp *rsp;
+	struct rnbd_msg_open msg;
+	struct rnbd_iu *iu;
+	struct kvec vec = {
+		.iov_base = &msg,
+		.iov_len  = sizeof(msg)
+	};
 
 	if (exists_devpath(pathname, sessname))
 		return ERR_PTR(-EEXIST);
@@ -1582,7 +1589,39 @@ struct rnbd_clt_dev *rnbd_clt_map_device(const char *sessname,
 		ret = -EEXIST;
 		goto put_dev;
 	}
-	ret = send_msg_open(dev, RTRS_PERMIT_WAIT);
+
+	rsp = kzalloc(sizeof(*rsp), GFP_KERNEL);
+	if (!rsp) {
+		ret = -ENOMEM;
+		goto del_dev;
+	}
+
+	iu = rnbd_get_iu(sess, RTRS_ADMIN_CON, RTRS_PERMIT_WAIT);
+	if (!iu) {
+		ret = -ENOMEM;
+		kfree(rsp);
+		goto del_dev;
+	}
+	iu->buf = rsp;
+	iu->dev = dev;
+	sg_init_one(iu->sgt.sgl, rsp, sizeof(*rsp));
+
+	msg.hdr.type    = cpu_to_le16(RNBD_MSG_OPEN);
+	msg.access_mode = dev->access_mode;
+	strscpy(msg.dev_name, dev->pathname, sizeof(msg.dev_name));
+
+	WARN_ON(!rnbd_clt_get_dev(dev));
+	ret = send_usr_msg(sess->rtrs, READ, iu,
+			   &vec, sizeof(*rsp), iu->sgt.sgl, 1,
+			   msg_open_conf, &errno, RTRS_PERMIT_WAIT);
+	if (ret) {
+		rnbd_clt_put_dev(dev);
+		rnbd_put_iu(sess, iu);
+		kfree(rsp);
+	} else {
+		ret = errno;
+	}
+	rnbd_put_iu(sess, iu);
 	if (ret) {
 		rnbd_clt_err(dev,
 			      "map_device: failed, can't open remote device, err: %d\n",